1. Field of the Invention
The present invention relates to a signal processing apparatus, a signal processing method, and a reception system. More particularly, the invention relates to a signal processing apparatus, a signal processing method, and a reception system adapted to reduce the scale of circuitry and lower power dissipation.
2. Description of the Related Art
Recent years have witnessed widespread use of a modulation scheme called orthogonal frequency division multiplexing (OFDM) for transmitting digital signals. The OFDM scheme involves having numerous orthogonal subcarriers furnished within the transmission bandwidth and assigning data to the amplitude and phase of each of the subcarriers for digital modulation through PSK (Phase Shift Keying) and QAM (Quadrature Amplitude Modulation). OFDM time domain signals are transmitted in units of symbols called OFDM symbols.
The OFDM scheme is applied extensively to terrestrial wave digital broadcasts that are highly susceptible to multipath interference. The terrestrial wave digital broadcasts adopting the OFDM scheme are subject to standards such as DVB-T (Digital Video Broadcasting-Terrestrial) and ISDB-T (Integrated Services Digital Broadcasting-Terrestrial).
Meanwhile, ETSI (European Telecommunication Standard Institute) is currently working on DVB (Digital Video Broadcasting)-T2 as a next-generation terrestrial digital broadcasting standard (see “DVB Bluebook A122 Rev. 1, Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2); disclosed at the DVB website updated Sept. 1, 2008; called the non-patent document 1 hereunder).
According to DVB-T2, data is transmitted in units of transmission frames called T2 frames. Also according to DVB-T2, the T2 frame is transmitted multiplexed with a signal called FEF (Future Extension Frame) having a structure different from that of the T2 frame.
Generally, upon receipt of a signal stream transmitted multiplexed with signals each having a different structure based on a different scheme, reception apparatuses each compatible with a different signal type detect and receive the corresponding signal independently. Under DVB-T2, a reception apparatus for receiving T2 frames and a reception apparatus for receiving FEFs detect and receive the relevant signal independently.
FIG. 1 is a schematic view showing a typical frame structure according to DVB-T2.
Under DVB-T2, as indicated in FIG. 1, T2 frames and FEF parts are multiplexed when transmitted. Specifically, each FEF part multiplexed with T2 frames has a predetermined length (FEF length) and is transmitted at predetermined intervals (FEF intervals) each made up of a plurality of T2 frames.
The T2 frames and FEF parts each have a P1 OFDM symbol (which may simply be called the symbol hereunder). P1, along with P2 to be discussed later, is a preamble signal that contains information necessary for such processing as demodulation of the OFDM signal.
P1 has identification information error-correcting-coded therein (i.e., it holds signaling information) for determining whether the frame in question is a T2 frame or an FEF part.
It follows that the reception apparatus for receiving T2 frames and the reception apparatus for receiving FEF parts can each detect T2 frames or FEF parts for demodulation by acquiring the information contained in P1 while excluding the influence of the irrelevant elements for enhanced demodulation performance.
When a given frame is a T2 frame, P1 holds other signaling information. This information, desired for demodulation purposes, typically includes the FFT size for performing FFT computations of symbols other than P1 (i.e., FFT size is the number of samples (symbols) subject to a single FFT computation). That is, if the frame of interest is a T2 frame, then P1 includes such information as the FFT size and transmission mode necessary for demodulating P2. It follows that to demodulate P2 desires demodulating P1 first.
In the T2 frame, the P1 symbol is followed by P2 symbols, symbols called “Normal” each, and a symbol called FC (Frame Closing), in that order.
Each OFDM symbol is generally made up of an effective symbol and a guard interval. The effective symbol constitutes a signal period in which IFFT is carried out upon demodulation. The guard interval is formed by having a partial waveform of the latter portion of the effective symbol copied unmodified to the beginning of the effective symbol. In FIG. 1, each guard interval is indicated as GI; P1 does not have any GI.
P2 holds L1 pre-signaling (L1 PRE) and L1 post-signaling (L1 POST).
The L1 pre-signaling includes information necessary for demodulating the L1 post-signaling. The L1 post-signaling includes information desired by each reception apparatus for access to the physical layer (i.e., to the layer pipes).
The L1 pre-signaling includes such information as the GI length, a pilot pattern (PP) representative of pilot signal locations indicating which symbols (subcarriers) contain pilot signals as known signals, the presence or absence of a transmission bandwidth extension (BWT_EXT) for transmitting the OFDM signal, and the number of OFDM symbols included in one T2 frame (NDSYM). These pieces of information included in the L1 pre-signaling constitute information necessary for demodulating data symbols (including FC).
The L1 pre-signaling further includes information giving more details of an FEF duration (FEF length, FEF interval, etc., shown in FIG. 1), as well as related information indicative of the FEF type (FEF_Type).
Thus the reception apparatus for receiving T2 frames and the reception apparatus for receiving FEFs can each detect T2 frames or FEF parts with more precision for demodulation purposes by acquiring the information from within P2, at the same time excluding more accurately the influence of the irrelevant elements for enhanced demodulation performance.
In the example of FIG. 1, two P2s are shown located in one T2 frame. In practice, each T2 frame may accommodate 1 through 16 P2s as OFDM symbols.